This nonprovisional application claims priority under 35 U.S.C. xc2xa7119(a) on Patent Application Nos. 2001-391037 and 2001-391038, each filed in Japan on Dec. 25, 2001. The entirety of each of the above documents is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an internal combustion engine, which is suitable as a power unit for a vehicle.
2. Description of Background Art
An internal combustion engine used for a motorcycle in the background art has been disclosed in Japanese Patent No. 2858017. In the internal combustion engine in the background art, the center line of the crankshaft is disposed on the center plane of the vehicle body along the longitudinal direction. A clutch and a gear shifter are disposed on one of the left and the right sides below the crankshaft. Furthermore, an auxiliary drive system including a starting motor, an electric generator, and the like is disposed on the other side. The mainshaft and the countershaft of the gear shifter including a transmission gear set are disposed in parallel with the crankshaft, but rearwardly of the crankshaft in the axial direction. A transmission case for accommodating these members is connected to the back of the crankcase.
In the internal combustion engine in the background art, a clutch having a large diameter is disposed on one of the left and the right sides on the center plane of the vehicle body, and the electric generator is disposed on the other side. Therefore, the width of the internal combustion engine increases, and thus the knee-grip capability is lowered. In addition, since a transmission case for accommodating a gear shift is provided rearwardly of the crankcase, the lengthwise dimension of the internal combustion engine increases, and thus in-vehicle mountability decreases.
In addition, in the internal combustion engine in the background art, the mainshaft and the countershaft of a gear shifter having a transmission gear set are disposed in parallel with the crankshaft. However, the axial position thereof is rearwardly of the crankshaft. Furthermore, a transmission case for accommodating these members is connected to the back of the crankcase. As a consequence, when intended to mount the internal combustion engine with the crankshaft oriented lengthwise on the motorcycle, the dimension of the wheelbase increases, which is not preferable.
In the present invention, the width of the internal combustion engine is reduced, and the axial length is shortened. Accordingly, the knee-grip capability is improved when the internal combustion engine is mounted on the vehicle, and the mounting capability is increased. In addition, the present invention intends to improve the assembling capabilities by applying some other modifications.
Having solved the aforementioned problems, according to a first aspect of the present invention, an internal combustion engine includes a crankshaft, a mainshaft of a transmission for holding a transmission gear train, a clutch disposed on the extension of the mainshaft, and a countershaft of the transmission for holding a gear train to be meshed with the aforementioned transmission gear train. The power is transmitted in order from the crank shaft to the clutch, the main shaft, and the countershaft. In addition, the mainshaft is disposed substantially directly below the crankshaft.
In the above structure, the mainshaft is disposed substantially directly below the crankshaft and the clutch having a large diameter is connected on the forward extension of the mainshaft. In addition, the clutch having a large diameter is positioned at the widthwise center when the internal combustion engine is viewed from the front, or in the direction along the crankshaft. Accordingly, the lateral width of the internal combustion engine may be reduced.
According to a second aspect of the present invention, at least a part of the mainshaft is disposed at the same axial position as the crankshaft. In other words, the mainshaft and the crank shaft are superimposed with each other when viewed from a certain position on the side of the shaft. Therefore, the axial length of the internal combustion engine may be reduced in comparison with the internal combustion engine in Japanese Patent No. 2858017. It also has such effect that oil dropped after lubricating the piston or the crank may be used for lubricating the gear set of the mainshaft.
According to a third aspect of the present invention, a crank chamber is defined by upper and a lower case members, the crankshaft is held between the upper and the lower case members, the mainshaft is adapted to be attached on the lower case member, and at least a part of the crank bearing and the main bearing are shifted with each other so as to be located at the different axial positions. This arrangement allows reduction of the length of the bolt for securing the bearing section for the crankshaft, which contributes to the improvement of workability.
According to a fourth aspect of the present invention, the internal combustion engine is mounted on a motorcycle with the crankshaft oriented lengthwise of the vehicle. Such positional relation between the vehicle and the internal combustion engine allows a reduction of the front projected area of the vehicle, and ensures better knee-grip. In addition, since the lengthwise dimension of the internal combustion engine is shortened, in-vehicle mountability is improved.
According to the fifth aspect of the present invention, the internal combustion engine is a V-type internal combustion engine. In this arrangement, the vertical height of the central portion of the internal combustion engine can be reduced, and thus in-vehicle mountability is improved.
In addition, in order to reduce the entire length of the internal combustion engine in the direction of the axis of the crankshaft, it is required to dispose the crankshaft and the transmission shafts such as a mainshaft at almost the same position in the axial direction. Therefore, it is required to accommodate the transmission shaft and a cam-type torque damper disposed on the extension of the mainshaft in the crankcase. The present invention is intended especially to improve in-vehicle mountability by reducing the length of the cam-type torque damper and shortening the axial length of the internal combustion engine while satisfying the above-described conditions. Furthermore, the present invention is intended to improve the assembly by applying some additional improvements.
Further to the above, according to a sixth aspect of the present invention, an internal combustion engine includes a crankshaft, a mainshaft of a transmission for holding a transmission gear train, a clutch disposed on the axis of the mainshaft, a cam-type torque damper to be disposed on the axis of the mainshaft, and a countershaft of the transmission for holding a gear train to be meshed with the transmission gear train. Power is transmitted in order from the crankshaft to the clutch, the cam-type torque damper, the mainshaft, and the countershaft. Furthermore, a mainshaft and a cam-type torque damper are disposed downwardly of the crankshaft in the crankcase.
According to the sixth aspect of the present invention, the mainshaft is disposed downwardly of the crankshaft. Accordingly, the entire length of the internal combustion engine in the direction of the crankshaft may be reduced in comparison with the internal combustion engine disclosed in Japanese Patent No. 2858017 in which the mainshaft is disposed rearwardly of the crankshaft. In addition, the mainshaft is disposed downwardly of the crankshaft. Accordingly, the mainshaft and the gear shifter continuing therefrom can be accommodated in the crankcase. Therefore, the need to provide a transmission case may be eliminated. Furthermore, the mainshaft and the cam-type torque damper are disposed downwardly of the crankshaft. Accordingly, oil dropped after lubricating the piston or the crank may be used for lubricating the gear set of the mainshaft or the cam-type torque damper.
According to a seventh aspect of the present invention, a bearing between the clutch and the cam-type torque damper is secured to the crankcase via a bearing holding member. In the arrangement of the present invention, since the cam-type torque damper may be assembled through a hole opened on the crankcase for mounting the bearing holding portion with the bearing holding member removed, assembly of the cam-type torque damper can be improved.
According to an eighth aspect of the present invention, the engine is mounted on the motorcycle with the crankshaft oriented lengthwise of the vehicle. The entire length of the internal combustion engine in the direction of the crankshaft is shortened. Accordingly, the length of the wheelbase of the vehicle can be shortened by mounting the crankshaft lengthwise of the vehicle.
According to a ninth aspect of the present invention, the internal combustion engine is a V-type internal combustion engine. In this arrangement, the vertical height of the central portion of the internal combustion engine may be reduced, and thus in-vehicle mountability may be improved.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.